1.目录结构
  assets/             contains assets definition
  commands/           contains console commands (controllers)
  config/             contains application configurations
  controllers/        contains Web controller classes
  mail/               contains view files for e-mails
  models/             contains model classes
  runtime/            contains files generated during runtime
  tests/              contains various tests for the basic application
  vendor/             contains dependent 3rd-party packages
  views/              contains view files for the Web application
  web/                contains the entry script and Web resources

2.yii系统对象


Models, Views, and Controllers
Models数据源，通常是数据库. 
View 展示数据的. 
Controllers接受请求和相应输出.

Components
组件是可重用的模块，组件仅仅包含逻辑。例如，一个组件可以是重量单位转换。

Application components
app组件是整个应用中的实例，是单实例的。

Widgets
挂件，是可重用的，包含逻辑和数据展示的功能


Filters
过滤器
Filters are objects that run before or after the execution of the Controller actions.

Modules
模块
You can consider Modules as reusable subapps, containing Models, Views, Controllers, and so forth.

Extensions
扩展
Extensions are packages that can be managed by the Composer.